Methods, apparatuses, and uses for infusion pump fluid pressure and force detection

ABSTRACT

An occlusion detection system detects an occlusion in a fluid path of an infusion pump. The infusion pump is for delivering fluid to a user. The infusion pump includes a housing, a motor, a reservoir, one or more drive train components, a sensor, and an electronics system. The motor is contained within the housing. The reservoir contains the fluid to be delivered. The one or more drive train components react to stimulus from the motor to force the fluid from the reservoir into the user. The sensor is positioned to measure a parameter associated with the motor or a drive train component, and the sensor produces three or more output levels across a range of measurements. The electronics system processes the senor output levels to declare when an occlusion exists.

RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication Serial No. 60/243,392, filed Oct. 26, 2000, entitled,“IMPROVED METHODS AND APPRATUSES FOR DETECTION OF FLUID PRESSURE”; andU.S. Provisional Patent Application Serial No. 60/192,901, filed Mar.29, 2000, entitled, “PRESSURE SENSING SYSTEM AND METHOD FOR DRUGDELIVERY DEVICES”, which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to improvements in infusion pumps suchas those used for controlled delivery of fluid to a user. Morespecifically, this invention relates to improved methods and apparatusesfor detecting fluid pressure and occlusions in fluid delivery paths ofinfusion pump systems.

BACKGROUND OF THE INVENTION

Infusion pump devices and systems are relatively well-known in themedical arts, for use in delivering or dispensing a prescribedmedication such as insulin to a patient. In one form, such devicescomprise a relatively compact pump housing adapted to receive a syringeor reservoir carrying a prescribed medication for administration to thepatient through infusion tubing and an associated catheter or infusionset.

A typical infusion pump includes a housing, which encloses a pump drivesystem, a fluid containment assembly, electronics system, and a powersupply. The pump drive system typically includes a small motor (DC,stepper, solenoid, or other varieties) and drive train components suchas gears, screws, and levers that convert rotational motor motion to atranslational displacement of a stopper in a reservoir. The fluidcontainment assembly typically includes the reservoir with the stopper,tubing, and a catheter or infusion set to create a fluid path forcarrying medication from the reservoir to the body of a user. Theelectronics system regulates power from the power supply to the motor.The electronics system may include programmable controls to operate themotor continuously or at periodic intervals to obtain a closelycontrolled and accurate delivery of the medication over an extendedperiod. Such pump drive systems are utilized to administer insulin andother medications, with exemplary pump constructions being shown anddescribed in U.S. Pat. Nos. 4,562,751; 4,678,408; 4,685,903; 5,080,653and 5,097,122, which are incorporated by reference herein.

Infusion pumps of the general type described above have providedsignificant advantages and benefits with respect to accurate and timelydelivery of medication or other fluids over an extended period comparedto manual syringe therapy. The infusion pump can be designed to beextremely compact as well as water resistant, and may be adapted to becarried by the user, for example, by means of a belt clip or a harness.As a result, precise amounts of medication may be automaticallydelivered to the user without significant restriction on the user'smobility or life-style, including in some cases the ability toparticipate in water sports.

In the past, medication infusion pump drive systems have included alarmsystems designed to detect and indicate a pump malfunction and/ornon-delivery of the medication to the patient due to a fluid pathocclusion. Such alarm systems have typically used a limit switch todetect when the force applied to the reservoir stopper reaches a setpoint. One known detector uses an “on/off” limit switch. When a setpoint is reached, the switch changes state (from open to closed or visaversa) triggering an alarm to warn the user. In U.S. Pat. No. 4,562,751,the limit switch is positioned at one end of a rotatable lead screw. Theforce applied to the limit switch by the lead screw is proportional tothe pressure applied to the medication as a result of power supplied tothe drive system to advance the stopper.

When an occlusion develops in the fluid path, the first consequence isthe lack of medication delivery, or “under-dosing.” But, a potentiallymuch greater danger arises from “over-dosing” due to an occlusionbreaking free after pressure has built up in the fluid path. Forexample, if a drive system continues to receive commands to delivermedication when the fluid path is blocked, fluid pressure may continueto grow until the occlusion is forced out, which then causes a lot orthe previously commanded medication to be expelled at once underpressure. This could result in an “over dose.” Thus, early detection ofan occlusion minimizes the potential for “over-dosing.”

However, the use of an on/off limit switch as an occlusion detector hasseveral disadvantages. The lead screw or other drive mechanism generallymoves axially some distance to actuate the limit switch. If themedication is highly concentrated, and small incremental deliveries arerequired, such as 0.5 micro liters, then the required stopperdisplacement per delivery is very small. When an occlusion develops, thelead screw displacement toward the limit switch is also small.Therefore, many deliveries may be missed before the lead screw isdisplaced sufficiently to actuate the limit switch.

Additionally, a limit switch typically has only one set point. Noise,temporary pressure fluctuations during a delivery, and temperatureand/or humidity effects may trigger false occlusion alarms. If the setpoint were placed higher to avoid some of the false detections,additional time would be required to detect a genuine occlusion.

SUMMARY OF THE DISCLOSURE

According to an embodiment of the invention, an occlusion detectionsystem for detecting an occlusion in a fluid path of an infusion pumpwith a reservoir containing fluid for delivering fluid to a userincludes a housing, a motor, a reservoir, one or more drive traincomponents, a sensor, and an electronics system. The motor is containedwithin the housing, and the one or more drive train components react tostimulus from the motor to force fluid from a reservoir into the user.The sensor is positioned to measure a parameter associated with themotor or a drive train component, and the sensor produces three or moreoutput levels across a range of measurements. The electronics systemprocesses the three or more sensor output levels to declare when anocclusion exists.

In preferred embodiments, the sensor measures a force proportional to aforce applied to a drive train component. In particular embodiments, thedrive train component is a lead screw. In other particular embodiments,the drive train component is a slide.

In alternative embodiments, the sensor measures tension or compressionon a beam proportional to a torque applied to the motor. In particularembodiments, the drive train component is a beam. In other particularembodiments, the drive train component is one or more mounts.

In other alternative embodiments, the sensor measures tension orcompression proportional to a pressure applied to a drive traincomponent. In particular embodiments, the drive train component is abellows. In other particular embodiments the drive train component is acap.

In preferred embodiments, the sensor is a force sensitive resistor. Inalternative embodiments, the sensor is a capacitive sensor. In otheralternative embodiments, the sensor is a strain gauge. In still otheralternative embodiments the sensor is a piezoelectric sensor.

In preferred embodiments, the electronics system uses a maximummeasurement threshold method to declare when an occlusion exists. Inparticular embodiments, a measurement threshold is at least 2.00 pounds.

In alternative embodiments, the electronics system uses a slopethreshold method to declare when an occlusion exists. In particularembodiments, a slope threshold is about 0.05 pounds per measurement.

In other alternative embodiments, the electronics system uses a maximummeasurement threshold method, and a slope threshold method to declarewhen an occlusion exists. In still other alternative embodiments, one ormore measurements must exceed a minimum level to declare that anocclusion exists.

In preferred embodiments, the measured parameter is correlated with afluid pressure in the reservoir. In particular embodiments, theelectronics system processes the sensor output levels to determine whenthe reservoir is empty. In other particular embodiments, the electronicssystem processes the sensor output levels to determine when a stoppercontacts an end of the reservoir. In still other particular embodiments,the electronics system processes the sensor output levels to determinewhen a slide is seated in a stopper.

In preferred embodiments, the sensor is positioned between the motor anda housing component. In particular embodiments, VHB adhesive ispositioned between the motor and the housing component. In otherparticular embodiments, one or more components including the sensor arestacked between the motor and the housing component, and the housingcomponent is positioned to remove space between the one or morecomponents before the housing component is attached to the housing. Inalternative embodiments, one or more components including the sensor arestacked between the motor and the housing, and back-fill material isinjected through the housing to remove space between the one or morecomponents and to fill the space between the one or more components andthe housing.

According to an embodiment of the invention, a method of detecting anocclusion in an infusion pump for infusing fluid into the body of a userincludes the steps of obtaining a measurement from a sensor before eachfluid delivery, calculating a slope of a line generated using two ormore measurements, comparing the slope to a slope threshold,incrementing a counter when the slope exceeds the slope threshold, anddeclaring an occlusion when the counter exceeds a detection count

According to another embodiment of the invention, a method of detectingan occlusion in an infusion pump for infusing fluid into the body of auser includes the steps of obtaining a measurement from a sensor beforeeach fluid delivery, calculating a current slope of a line using two ormore measurements, calculating an average slope using a previous averageslope and the current slope, comparing the average slope to a slopethreshold, incrementing a counter when the average slope exceeds theslope threshold, and declaring an occlusion when the counter exceeds adetection count value. In preferred embodiments, the two or moremeasurements are not consecutive.

According to another embodiment of the invention, an occlusion detectionsystem for detecting an occlusion in a fluid path of an infusion pumpwith a reservoir containing fluid for delivering fluid to a userincludes, a housing, forcing means for forcing fluid from a reservoircontaining a fluid, sensing means for sensing a parameter associatedwith the forcing means for forcing fluid from the reservoir containingthe fluid to obtain one or more measurements, and evaluation means. Thesensing means producing one of three or more output levels for each ofthe one or more the measurements. The evaluation means evaluates the oneof three or more output levels associated with each of the one or moremeasurements to declare when an occlusion exists.

Other features and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, variousfeatures of embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front, perspective view of an infusion pump, according to anembodiment of the present invention.

FIG. 2 is a rear view of the infusion pump of FIG. 1, with a rear dooropen to illustrate particular internal components.

FIG. 3 is an illustration view of a drive system of the infusion pump ofFIG. 1.

FIG. 4 is an illustration view of an infusion pump drive system with asensor according to a second embodiment of the present invention.

FIG. 5 is an illustration view of an infusion pump drive system with asensor according to a third embodiment of the present invention.

FIG. 6(a) is a cross-sectional view of a sensor mounted between a drivesystem component and a housing according to a first and secondembodiment of the present invention as shown in FIGS. 3 and 4.

FIG. 6(b) is a cross-sectional view of a force sensitive resistor stylesensor according to a fourth embodiment of the present invention.

FIG. 7(a) is an exploded bottom/front perspective view of an infusionpump drive system, sensing system, and fluid containing assembly,incorporating the sensor of FIG. 6(b).

FIG. 7(b) is an exploded top/front perspective view of the infusion pumpdrive system, sensing system, and fluid containing assembly of FIG.7(a).

FIG. 7(c) is a cross-sectional side view of an assembled infusion pumpdrive system, sensing system, and fluid containing assembly of FIG.7(b).

FIG. 7(d) is an enlarged cross-sectional side view of the sensing systemshown as 7 (d) in FIG. 7(c).

FIG. 8(a) is a top view of a disk of the sensing system of FIGS.7(a)-(d).

FIG. 8(b) is a side view of the disk of the sensing system of FIGS.7(a)-(d).

FIG. 8(c) is a bottom view of the disk of the sensing system of FIGS.7(a)-(d).

FIG. 9 is an enlarged, cross-sectional view of a sensor system accordingto a fifth embodiment of the present invention.

FIG. 10 is a graph showing measured voltage across the force sensitiveresistor of FIG. 6(b) as a function of applied force.

FIG. 11 is a graph showing measured voltage across the force sensitiveresistor of FIG. 6(b) during operation of the drive system shown inFIGS. 7(a)-(d).

FIG. 12 is a cross sectional view of a capacitive sensor mounted betweena drive system component and a housing according a sixth embodiment ofthe present invention.

FIG. 13 is a cross-sectional view of a capacitive sensor according aseventh embodiment of the present invention.

FIG. 14(a) is a side plan view of a multi-switch sensor, where theswitches are mounted in series and are individually electricallymonitored according to an eighth embodiment of the present invention.

FIG. 14(b) is a side plan view of a multi-switch sensor, where theswitches are mounted in series and are electrically connected in seriesaccording to a ninth embodiment of the present invention.

FIG. 14(c) is an electrical schematic for a multi-switch sensor, wherethe switches are electrically connected in series according to a tenthembodiment of the present invention.

FIG. 15(a) is a top plan view of a multi-switch sensor, where theswitches are mounted in parallel.

FIG. 15(b) is a side plan view of the multi-switch sensor of FIG. 15(a).

FIG. 15(c) is an electrical schematic for a multi-switch sensor, wherethe switches are electrically connected in parallel.

FIG. 16 is an illustration view of a sensor in a pump drive systemaccording to an eleventh embodiment of the present invention.

FIG. 17 is an illustration view of a sensor in a pump drive systemaccording to a twelfth embodiment of the present invention.

FIG. 18 is an illustration view of a sensor in a pump drive systemaccording to a thirteenth embodiment of the present invention.

FIG. 19 is an illustration view of a sensor in a pump drive systemaccording to fourteenth embodiment of the present invention.

FIG. 20 is an illustration view of a sensor in a pump drive systemaccording to a twentieth embodiment of the present invention.

FIG. 21 is an illustration view of the infusion pump drive system ofFIG. 4 showing certain torque forces.

FIG. 22(a) is a perspective view of a sensor in a portion of a drivesystem according to a twenty-first embodiment of the present invention.

FIG. 22(b) is a rear view of the sensor and pump drive system of FIG.22(a).

FIG. 23 is an illustration view of a sensor in a portion of a pump drivesystem according to a twenty-second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the drawings for purposes of illustration, the invention isembodied in a pressure sensing system for an infusion pump. The infusionpump is used for infusing fluid into the body of a user. In preferredembodiments, the infused fluid is insulin. In alternative embodiments,many other fluids may be administered through infusion such as, but notlimited to, HIV drugs, drugs to treat pulmonary hypertension, ironchelation drugs, pain medications, anti-cancer treatments, medications,vitamins, hormones, or the like.

In preferred embodiments, a programmable controller regulates power froma power supply to a motor. The motor actuates a drive train to displacea slide coupled with a stopper inside a fluid filled reservoir. Theslide forces the fluid from the reservoir, along a fluid path (includingtubing and an infusion set), and into the user's body. In preferredembodiments, the pressure sensing system is used to detect occlusions inthe fluid path that slow, prevent, or otherwise degrade fluid deliveryfrom the reservoir to the user's body. In alternative embodiments, thepressure sensing system is used to detect when: the reservoir is empty,the slide is properly seated with the stopper, a fluid dose has beendelivered, the infusion pump is subjected to shock or vibration, theinfusion device requires maintenance, or the like. In furtheralternative embodiments, the reservoir may be a syringe, a vial, acartridge, a bag, or the like.

In general, when an occlusion develops within the fluid path, the fluidpressure increases due to force applied on the fluid by the motor anddrive train. As power is provided to urge the slide further into thereservoir, the fluid pressure in the reservoir grows. In fact, the loadon the entire drive train increases as force is transferred from themotor to the slide, and the slide is constrained from movement by thestopper pressing against the fluid. An appropriately positioned sensorcan measure variations in the force applied to one or more of thecomponents within the drive train. The sensor provides at least threeoutput levels so measurements can be used to detect an occlusion andwarn the user.

Early occlusion detection minimizes the time the user is withoutmedication and more importantly, minimizes the potential of overdosingcaused when an occlusion breaks free and fluid rushes into the user'sbody to relieve the built up pressure from the reservoir. In preferredembodiments, an occlusion is detected before the pressure is high enoughto deliver a dose greater than a maximum allowable bolus. Generally, themaximum allowable bolus is the maximum amount of fluid that may bedelivered safely into the user at one time, which depends on theconcentration of ingredients in the fluid, the sensitivity of the userto the fluid, the amount of fluid that the user presently needs, theamount of fluid still available in the user from previous deliveries, orthe like. The pressure in the reservoir, or the force on the drive traincomponents, associated with the maximum allowable bolus depends on thediameter of the reservoir, leverage in the drive train, friction, andthe like.

In preferred embodiments, as shown in FIGS. 1-3, an infusion pump 101includes a reservoir 104, a slide 109, a drive system 138, aprogrammable controller 113, and a power supply (not shown), allcontained within a housing 102. The housing 102 has a rear door 120,which may be pivoted open to provide access to the interior of the pump101 for removing and replacing the reservoir 104 and the slide 109 (FIG.2 shows the rear door 120 pivoted to an open position).

The fluid-containing reservoir 104 includes a reservoir barrel 105, aneck 106, and a head 103, which are generally concentrically aligned.The neck 106, which has a smaller diameter than the barrel 105, connectsa front end of the barrel 105 to the head 103. The neck 106 seats withinan outlet port 107 formed in the housing 102. The head 103, which has alarger diameter than the neck 106, extends through the housing 102. Thehead 103 mates with tubing 110 by means of a fitting 108, therebyestablishing fluid communication from the barrel 105, through thehousing 102, and into the tubing 110. The tubing 110 extends from thefitting 108 to an infusion set 136, which provides fluid communicationwith the body of the user. A rear end of the barrel 105 forms an openingto receive the slide 109. Fluid is forced from the reservoir 104 as thedrive system 138 moves the slide 109 from the rear end of the barrel 105toward the front end of the barrel 105.

The drive system 138, best shown in FIG. 3, includes a motor 111, acoupler 121, a lead screw 117, a drive nut 116, and one or more latcharms 119. The motor 111 is coupled to the lead screw 117 by the coupler121. The motor rotates the coupler 121, which in turn rotates the leadscrew 117. The drive nut 116 includes a bore with internal threads (notshown). External threads on the lead screw 117 mesh with the internalthreads on the drive nut 116. As the lead screw 117 rotates in responseto the motor 111, the drive nut 116 is forced to travel along the lengthof the lead screw 117 in an axial direction d. The one or more latcharms 119 are attached to the drive nut 116, and extend away from thedrive nut 116 to engage the slide 109, thereby coupling the slide 109 tothe drive nut 116. Thus, as the drive nut 116 is forced to translatealong the length of the lead screw 117 in axial direction d, the slide109 is forced to translate parallel to the lead screw 117 in an axialdirection d′.

Power is supplied to the motor 111 by the power supply (not shown), inresponse to commands from the programmable controller 113. Preferably,the motor 111 is a solenoid motor. Alternatively, the motor may be a DCmotor, AC motor, stepper motor, piezoelectric caterpillar drive, shapememory actuator drive, electrochemical gas cell, thermally driven gascell, bimetallic actuator, or the like. In alternative embodiments, thedrive train includes one or more lead screws, cams, ratchets, jacks,pulleys, pawls, clamps, gears, nuts, slides, bearings, levers, beams,stoppers, plungers, sliders, brackets, guides, bearings, supports,bellows, caps, diaphragms, bags, heaters, or the like. Preferably, thepower supply is one or more batteries. Alternatively, the power supplymay be a solar panel, capacitor, AC or DC power supplied through a powercord, or the like.

The programmable controller 113 may be programmed by a care providersuch as a physician or trained medical personnel, or by the user. Inpreferred embodiments, programming is conducted using an array ofbuttons 114 and a display 115 located on a face of the housing 102. Thedisplay 115 provides information regarding program parameters, deliveryprofiles, pump operation, alarms, warnings, statuses, or the like. Inpreferred embodiments, the programmable controller 113 operates themotor 111 in a stepwise manner, typically on an intermittent basis; toadminister discrete precise doses of the fluid to the user according toprogrammed delivery profiles. In alternative embodiments, theprogrammable controller operates the motor continuously.

In preferred embodiments of the present invention, the lead screw 117includes a support pin 130 that extends through one or more bearings 132and maintains contact with a sensor 134 positioned to detect forcesapplied by the lead screw 117 along the axis of the lead screw 117. Theone or more bearings 132 and the coupler 121 are designed to allow thelead screw some translational freedom of movement along its axis whileproviding lateral support. The sensor 134 is therefore subjected to allaxial forces applied to the lead screw 117 in the direction away fromthe motor 111. The axial force exerted by the lead screw 117 on thesensor 134 is generally correlated with the fluid pressure in thereservoir 109. For example, if an occlusion developed within the fluidpath, blocking fluid delivery from the infusion pump to the body of theuser, the fluid pressure would increase as the slide 109 is forcedforward by the drive system 138. Each time the programmable controller113 commands power to be supplied to the motor 111, the slide 109 isdriven forward into the reservoir 104, therefore increasing the fluidpressure. The fluid pressure is partially relieved by compliance in thesystem, for example, expansion of the tubing 110 and the reservoir 109,deformation of one or more O-ring seals 140 on the slide 109, or thelike. The remaining pressure is exerted against the slide 109, forcingit to back out of the reservoir 104. But the slide 109 is prevented frommoving by the one or more latch arms 119. The latch arms 119 transferthe force from the slide 109 to the drive nut 116, which in turntransfers the force, by way of thread engagement, to the lead screw 117.The sensor 134 is then subjected to a force with a magnitude correlatedwith the fluid pressure. Preferably, the sensor 134 provides at leastthree output levels across the magnitude of sensed forces. Anelectronics system (not shown) supports the sensor 134 by providingpower and/or signal processing, depending on the type of sensor 134.

In alternative embodiments, a motor 401 (or a motor with an attachedgear box) includes a drive shaft 402, which drives a set of gears 403,as shown in FIG. 4. A lead screw 404 concentrically aligned with a gear412 in the set of gears 403 is coupled to rotate with the gear 412. Ahollow slide 405 includes an internally threaded bore 416 that passesthrough a rear end 418 of the slide 405, and engages with externalthreads of the lead screw 404. The axis of the slide 405 is generallyparallel to the axis of the lead screw 404. The slide 405 furtherincludes a tab (not shown) that engages a groove (not shown) in ahousing (not shown) that runs parallel to the lead screw 404 to preventthe slide 405 from rotating when the lead screw 404 rotates. Thus, asthe lead screw 404 rotates, the slide 405 is forced to translate alongthe length of the lead screw 404. A front end 420 of the slide 405engages a stopper 406 inside a reservoir 407. As the slide 405 advancesdue to the rotation of the lead screw 404, the stopper 406 is forcedfarther into the reservoir 407, thus forcing fluid from the reservoir407, through tubing 422, and through an infusion set 408. In alternativeembodiments, the stopper and slide are formed as one piece.

The lead screw 404 includes a support pin 414 that extends axially froman end of the lead screw 404 that is not enclosed within the slide 405.The support pin 414 passes through a bearing 409, and maintains contactwith a sensor 410. The bearing 409 provides lateral support, and allowsthe lead screw 404 to have some axial translational displacement.However, the sensor 410 is positioned to prevent the lead screw 404 fromtranslational motion away from the reservoir 407. And therefore, thesensor 410 is positioned to sense forces applied to the lead screw 404in reaction to fluid pressure within the reservoir 407. The sensorprovides at least three output levels based on the measurement of thesensed forces.

In other alternative embodiments, an infusion pump 501 includes a motor502, gear box 506, drive screw 503, slide 504, stopper 507, and areservoir 505 generally aligned with each other to share a generallycommon concentric centerline, as shown in FIG. 5. The motor 502 rotatesthe drive screw 503 via a gear box 506. The drive screw 503 has externalthreads, which engage internal threads 522 on a cylindrical bore 520running most of the length of the slide 504. The slide 504 furtherincludes one or more tabs 514 that fit within one or more slots 516 in ahousing 518 to prevent the slide 504 from rotating with respect to thehousing 518. As the drive screw 503 rotates, the slide 504 is forced totravel along its axis. The slide 504 is in removable contact with astopper 507 within the reservoir 505. And, as the slide 504 advancesinto the reservoir 505, the stopper 507 is displaced forcing fluid outof the reservoir 505, through a fitting 508, through tubing 509, andthrough an infusion set (not shown). A sensor 511 is positioned betweenthe motor 502 in the housing 518 to detect forces translated from fluidpressure within the reservoir 505 through, the stopper 507, slide 504,drive screw 503, and the gear box 506 to the motor 502. The sensor 511provides at least three output levels based on the detected forces.Further alternative embodiments are described in detail in co-pendingapplication Ser. No. 09/429,352, filed Oct. 28, 1999, which isincorporated by reference herein.

In preferred embodiments, a sensor is a force sensitive resistor, whoseresistance changes as the force applied to the sensor changes. Inalternative embodiments, the sensor is a capacitive sensor,piezoresistive sensor, piezoelectric sensor, magnetic sensor, opticalsensor, potentiometer, micro-machined sensor, linear transducer,encoder, strain gauge, and the like, which are capable of measuringcompression, shear, tension, displacement, distance, rotation, torque,force, pressure, or the like. In preferred embodiments, the sensor iscapable of providing an output signal in response to a physicalparameter to be measured. And the range and resolution of the sensoroutput signal provides for at least three levels of output (threedifferent states, values, quantities, signals, magnitudes, frequencies,steps, or the like) across the range of measurement. For example, thesensor might generate a low or zero value when the measured parameter isat a minimum level, a high or maximum value when the measured parameteris at a relatively high level, and a medium value between the low valueand the high value when the measured parameter is between the minimumand relatively high levels. In preferred embodiments, the sensorprovides more than three output levels, and provides a signal thatcorresponds to each change in resistance in a sampled, continuous, ornear continuous manner. The sensor is distinguished from a switch, whichhas only two output values, and therefore can only indicate two levelsof output such as, ‘on’ and ‘off,’ or ‘high’ and ‘low.’

Preferred embodiments of the present invention employ a force sensitiveresistor as the sensor, which changes resistance as the force applied tothe sensor changes. The electronics system maintains a constant supplyvoltage across the sensor. The output signal from the sensor is a signalcurrent that passes through a resistive material of the sensor. Sincethe sensor resistance varies with force, and the supply voltage acrossthe sensor is constant, the signal current varies with force. The signalcurrent is converted to a signal voltage by the electronics system. Thesignal voltage is used as a measurement of force applied to a drivetrain component or fluid pressure in the reservoir. In alternativeembodiments, a constant supply current is used and the signal voltageacross the sensor varies with force (fluid pressure). In furtheralternative embodiments, other electronics systems and/or other sensorsare used to convert fluid pressure or forces into a measurement used bythe electronics system to detect occlusions in the fluid path.

In preferred embodiments, the force resistive sensor 706 has asubstantially planar shape and is generally constructed of a layer offorce resistive material 606 sandwiched between two conductive pads 607,which are sandwiched within protective outer layers 608, as shown inFIG. 6(b). Electrical leads 605 carry a sensor signal from theconductive pads 607 to the electronics system (not shown). In particularembodiments, the force resistive material layer 606 is a suspension ofconductive material in a polymer matrix. The conductive pads 607 andelectrical leads 605 are formed from one or more layers of conductiveink, such as silver ink, gold ink, platinum ink, copper ink, conductivepolymers, doped polymers, or the like. And the protective outer layers608 are polyester, which provide electrical insulation as well asprotection from the elements. A sensor 706 of the type shown in FIG.6(b) may be obtained under part number A101, from Tekscan Co. of SouthBoston, Mass. In alternative embodiments, the protective outer layersare made of other insulating materials such as Mylar, saran, urethane,resins, PVC, plastic, linen, cloth, glass, and the like. In otheralternative embodiments, the conductive pads and/or leads are sheets ofconductive material, wires, foil, or the like.

In preferred embodiments, the sensor 706 is positioned between flatrigid components to spread the force applied to the sensor 706 acrossthe entire sensor surface area. Preferably, the sensor 706 is locatedbetween two flat substantially rigid members, such as a housing and amotor.

In alternative embodiments, a sensor 601 is disposed between a rigidload plate 602 and a rigid back support 603, as shown in FIG. 6(a). Theload plate 602 is in contact with an end of a lead screw 604. Examplesof embodiments that use a lead screw to supply force to a sensor areshown in FIGS. 3 and 4. The back support 603 is generally secured inplace by the pump housing 609. Alternatively, a back support is notneeded and the sensor is placed against the pump housing. In otheralternative embodiments, the load plate is in contact with the motor oranother drive train component. In further alternative embodiments, alayer of adhesive (not shown) is placed between the sensor and a plateor component. In further alternative embodiments, force is applied toonly a portion of the sensor.

In preferred embodiments, the design and method for mounting the sensormust: sufficiently limit unintended movement of the slide with respectto the reservoir; minimize space between components; be rigid enough forthe sensor to immediately detect small changes in force; avoidpreloading the sensor to the point that the sensor range is insufficientfor occlusion, seating, and priming detection; provide sufficientresolution for early occlusion detection; compensate for sensor systemand drive train component dimensional tolerance stack-up; allowsufficient movement in components of the drive system to compensate formisalignments, eccentricities, dimensional inconsistencies, or the like;avoid adding unnecessary friction that might increase the power requiredto run the drive system; and protect the sensor from shock and vibrationdamage.

Generally, once the infusion set is primed and inserted into the user'sbody, the slide must not be permitted to move in or out of the reservoirunless driven by the motor. If the motor and/or drive train componentsare assembled in a loose configuration that allows the slide to movewithin the reservoir without motor actuation, then if the infusion pumpis jolted or bumped, fluid could be inadvertently delivered.Consequently, the sensor and/or components associated with mounting thesensor are generally positioned snugly against the drive train componentfrom which force is being sensed, thus preventing the drive traincomponent from moving when the infusion pump is subjected to shock orvibration.

In preferred embodiments, the sensor is positioned so that as soon asthe pump motor is loaded during operation, a drive train componentapplies a load to the sensor. Minimizing space between the sensor andthe load-applying drive train component improves the sensor'ssensitivity to load fluctuations. Small changes in load may be used todetect trends, and therefore provide an early warning that a blockage isdeveloping before the fluid delivery is stopped entirely.

In preferred embodiments, the sensor and associated electronics areintended to measure forces between 0.5 pounds (0.23 kg) and 5.0 (2.3 kg)pounds with the desired resolution of less than or equal to 0.05 pounds.Yet, the infusion pump including the sensor should survive shock levelsthat result in much higher forces being applied to the sensor than theintended sensor measurement range. In alternative embodiments, thesensor range is from zero to 10 pounds (4.5 kg). In other alternativeembodiments, the sensor range and/or resolution may be greater orsmaller depending upon the concentration of the fluid being delivered,the diameter of the reservoir, the force required to operate the drivetrain, the level of sensor noise, the algorithms applied to detecttrends from sensor measurements, or the like.

In preferred embodiments, to compensate for tolerance stack-up, thehousing includes a variably positioned housing component that may bevariably positioned with respect to a housing body. In particularembodiments, the variably positioned housing component is pressedagainst the sensor and/or sensor mounting components to remove gapsbetween the sensor, sensor mounting components and drive componentsbefore the variably positioned housing component is assembled with thehousing body. Thus, the tolerance stack up between components is removedby adjusting the volume within the housing during assembly.

In alternative embodiments, one or more compressible components are usedto compensate for tolerance stack up. In further alternativeembodiments, flowable materials such as foam, adhesive, filler, liquidmetal, plastic, microbeads, or the like are poured, injected, sprayed,forced, pumped, or the like, into the housing to substantially reducespace between the housing, sensor, sensor mounting components, and/ordrive components.

In preferred embodiments, the infusion pump 701 includes a housing 702,and a housing bottom 703 to enclose a drive system 730, a sensing system740, and a fluid containing assembly 750 as shown in FIGS. 7(a)-(d). Thedrive system 730 includes a motor assembly 705, a drive-screw 710, and aslide 711. The sensing system 740 includes a sensor 706, an adhesive pad707, a support disk 708, a housing cap 712, and an optional label 724.And the fluid containing assembly 750 includes a stopper 714, areservoir 715, and a reservoir connector 716.

The drive system 730 forces fluid out of the reservoir 715 in acontrolled and measured manner. The drive-screw 710 mates with threads717 internal to the slide 711. One or more tangs 718 on the slide 711ride inside groves 726 in the housing 702 that prevent the slide 711from rotating. The motor assembly includes a tang 721 that prevents themotor assembly 705 from rotating within the housing 702. Thus, when themotor assembly 705 is powered, the drive screw 710 rotates, and theslide 711 is forced to translate along its axis. A threaded tip 712 onthe slide 711 is detachably engaged with internal threads 713 on thestopper 714, as described in detail in co-pending application Ser. No.09/429,352, filed Oct. 28, 1999, which is incorporated by referenceherein. The stopper 714 is positioned to push fluid from inside thereservoir 715 through the reservoir connector 716 into tubing (notshown). The reservoir connector 716 seals the reservoir 715 in thehousing 702.

When the motor assembly 705 is inserted into the housing 702, a shoulder719 on the motor assembly 705 rests against a lip 720 formed on theinside of the housing 702. The lip 720 prevents the motor assembly 705from translating along its axis in the forward direction (toward thereservoir 715). The components of the sensing system 740 are stackedbehind the motor assembly 705, trapping the sensor 706 between the motorassembly 705 and components that are held in place by the housing bottom703. Once the housing bottom 703 is securely attached to the housing702, and the sensor system 740 is in place, the sensor 706 is subjectedto axial forces placed on the motor assembly 705 by components of thedrive system due to fluid pressure within the reservoir 715.

In preferred embodiments, during the assembly process, care is taken tosecure the motor assembly 705 against the lip 720, and essentiallyeliminate space between components of the sensor system that might allowthe motor assembly 705 to move away from the lip 720. Not attaching themotor assembly 705 directly to the lip 720 of the housing 702 allows themotor assembly 705 to pitch and yaw slightly as it operates, and allowsthe sensor 706 to be subjected to axial forces applied to the motorassembly 705.

In particular embodiments, the slide 711 is threaded onto the drivescrew 710, then the motor assembly 705 and slide 711 are slid into thehousing 702. The sensor 706 is then positioned on the motor assembly705. Next, the housing bottom 703 is securely welded to the housing 702.In alternative embodiments, the housing bottom 703 is permanentlyattached to the housing 702 using one or more adhesives, ultrasonicwelding, heat bonding, melting, snap fit, or the like. Once the housingbottom 703 is attached to the housing 702, the remaining components ofthe sensor system 740 are installed through a hole 704 formed in thehousing bottom 703. An adhesive pad 707 is placed on the sensor 706,followed by a rigid disk 708.

In preferred embodiments, the adhesive pad 707 serves several purposesaside from securing the disk 708 to the sensor 706. The adhesive pad 707material conforms to the surface to correct for surface irregularitieson the disk 708 and spread loads evenly across the sensor 706.Furthermore, the adhesive pad 707 has other properties such as a lowshear strength that allows the motor assembly 705 some freedom to pitchand yaw, provides shock absorption and/or vibration dampening, and doesnot substantially compress under the range of forces to be measured bythe sensor 706. In particular embodiments, the adhesive pad 707 is a0.010-inch thick layer of very high bond (VHB) acrylic adhesive. Inalternative embodiments, one or more other materials and/or thicknessesare used that provide adhesion and/or cushioning such as tapes, epoxies,glues, foams, rubber, neoprene, plastics, hot melts, or the like,depending on the space to be filled, the forces to be measured, the sizeand weight of components to be stacked together, the amount of freedomof movement needed, the shock and vibration requirements, or the like.

The disk 708 includes a generally cylindrical tang 722 extending fromthe center of the disk 708 away from the adhesive pad 707. The housingcap 712 includes a generally radially centered hexagonal bore 728 largeenough to receive the cylindrical tang 722. The circumference of thehousing cap 712 includes a beveled edge 725. The housing cap 712 isplaced onto the disk 708 so that the tang 722 is positioned in thehexagonal bore 728, and the beveled edge 722 is facing away from thedisk 708.

In preferred embodiments, the interior surface 726 (facing the disk 708)of the housing cap 712 includes ridges 723 that extend radially from oneor more of the flat edges of the hexagonal bore 728 to the circumferenceof the housing cap 712, as shown in FIGS. 8(a-b). The ridges 723 holdthe housing cap 712 away from the surface of the disk 708 to createspace for adhesive. Adhesive is inserted through the hexagonal bore 728,at each of the comers, where there is space between the hexagonal bore728 and the tang 722. Adhesive inserted at the hexagonal bore 728spreads radially out to the edges of the disk 708 and the housing cap712, filling the space between each of the ridges 723. In preferredembodiments, the housing cap 712 is clear so that an assembler canobserve the quality of the adhesive coverage between the housing cap 712and the disk 708, and so that ultraviolet-light-cured adhesive may beused.

In alternative embodiments, the bore in the housing cap has a shapeother than hexagonal, such as triangular, square, pentagonal, polygonal,circular, irregular, star shaped, or the like. In other alternativeembodiments, the tang on the disk may have other shapes, such astriangular, square, pentagonal, polygonal, circular, irregular, starshaped, or the like. In further alternative embodiments, other methodsmay be used to hold the housing cap off of the surface of the disk, suchas dimples, grooves, flutes, bumps, texturing, broken ridges, or thelike. In still further alternative embodiments, other bonding methodsmay be used such as epoxy, hot melt, tape, contact cement, otheradhesives, or the like.

In preferred embodiments, once the housing cap 712 is secured to thedisk 708, a force is applied to the housing cap 712 to assure that theshoulder 719 on the motor assembly 705 is seated against the lip 720 inthe housing 702, and that space between components stacked between themotor assembly 705 and the housing cap 708 is substantially removed. Theforce is then removed, so that sensor 706 is not subjected to a preload,and the housing cap 712 is bonded to the housing bottom 703. Preferably,adhesive is applied along the beveled edge 725 of the housing cap 712 tofill the space between the housing cap 712 and the housing bottom 703.Optionally, a label 724 is placed over the housing cap 712.

In alternative embodiments, several components are assembled togetherbefore being placed into the housing. For example, the motor assembly705, sensor 706, adhesive pad 707, and disk 708 may be assembledtogether and then placed into the housing 702 followed by the housingbottom 703 and then the housing cap 712. In other alternativeembodiments, fewer parts are used. For example, a sensor may include arigid backing obviating the need for a disk. Or a housing bottom may nothave an opening for a housing cap, so all of the components areinstalled into the housing and the housing bottom is positioned toremove spaces between the components and then secured to the housing. Instill further alternative embodiments, the force applied to remove spacebetween components is not removed before the housing cap is secured tothe housing bottom. In particular alternative embodiments, the preloadon the sensor is used to confirm that the space between the componentsis removed.

Although the foregoing describes one method of assembly, it can beappreciated by those skilled in the art that alternative assemblymethods may be employed without departing from the spirit of theinvention.

In alternative embodiments, a compressible member is used to compensatefor tolerance stack-up when assembling a sensor 907 with a motorassembly 906, as shown in FIG. 9. An infusion pump 901 includes ahousing bottom 903 attached to a housing 902, which encloses the motorassembly 906. The generally planar-shaped sensor 907 is positioned indirect contact with the motor assembly 906. The compressible member is aflexible silicone rubber seal 908 disposed between the outer edge of thesensor 907 and the housing bottom 903. Before assembly, the seal 908 isgenerally annular with a generally circular cross-section. When the seal908 is placed on the sensor 906, and the housing bottom 903 is welded orotherwise attached to the main housing assembly 902, the seal 908becomes deformed and adapts to the available space to form a waterresistant seal between the sensor 907 and the housing bottom 903. Thespace filled by the seal 908 varies due to the dimensional tolerancestack-up of drive train components (not shown), the sensor 907, thehousing 902, and the housing bottom 903. The housing bottom 903 includesan opening 904 generally in line with the axis of rotation of the motorassembly 906. A compliant back-fill material 909, such as silicone,urethane, hot melt adhesive, complaint epoxy, or the like, is injectedthrough the opening 904 to fill the space between the sensor 907 and thehousing bottom 903. The back-fill material 909 is substantiallyincompressible in the axial direction so that forces applied to thesensor 907 by the drive system are not relieved by the back-fillmaterial 909. Furthermore, the back-fill material 909 mechanicallyisolates the drive system from shock and vibration of the housing 902and housing bottom 903. In further alternative embodiments, one or morevents (not shown) are provided in the housing bottom 903 to permitventing of air and improve dispersion of the material 909 as thematerial 909 is injected into the center opening 904 and flows radiallyoutward to the seal 908. The seal 908 serves as a dam to prevent thematerial 909 from spreading around the motor assembly 906 and into otherareas within the housing 902. Once cured, the material 909 helps toabsorb shock loads, dampen vibrations, compensate for tolerancestack-up, resist water penetration, and provide an even loaddistribution across the sensor 907. Optionally, a label 910 is placed onthe exterior of the housing bottom 903 over the opening 904.

In preferred embodiments, the sensor and associated electronics providea relatively linear voltage output in response to forces applied to thesensor by one or more drive train components. Particular preferredembodiments employ the sensor 706 shown in FIGS. 6(b), and 7(a)-7(d). Anexample of measured voltages from the sensor 706, (and its associatedelectronics) in response to forces ranging from 0.5 pounds to 4.0pounds, are shown as data points 201-208 in FIG. 10.

In preferred embodiments, each sensor is calibrated by collectingcalibration points throughout a specified range of known forces, such asshown in FIG. 10. A measured voltage output for each known force isstored in a calibration lookup table. Then, during pump operation, thevoltage output is compared to the calibration points, and linearinterpolation is used convert the voltage output to a measured force.Preferably, eight calibration points are used to create the calibrationlookup table. Alternatively, more or fewer calibration points are useddepending on, the sensor linearity, noise, drift rate, resolution, therequired sensor accuracy, or the like. In other alternative embodiments,other calibration methods are used such as, curve fitting, a look uptable without interpolation, extrapolation, single point calibration, orthe like. In further alternative embodiments, the voltage output inresponse to applied forces is substantially non-linear. In furtheralternative embodiments, no calibrations are used.

In preferred embodiments, sensor measurements are taken just prior tocommanding the drive system to deliver fluid, and soon after the drivesystem has stopped delivering fluid. In alternative embodiments, sensordata is collected on a continuous basis at a particular sampling ratefor example 10 Hz, 3 Hz, once every 10 seconds, once a minute, onceevery five minutes, or the like. In further alternative embodiments, thesensor data is only collected just prior to commanding the drive systemto deliver fluid. In still further alternative embodiments, sensor datais collected during fluid delivery.

In preferred embodiments, two methods are employed to declare occlusionsin the fluid path, a maximum measurement threshold method, and a slopethreshold method. Either method may independently declare an occlusion.If an occlusion is declared, commands for fluid delivery are stopped andthe infusion pump provides a warning to the user. Warnings may includebut are not limited to, sounds, one or more synthesized voices,vibrations, displayed symbols or messages, lights, transmitted signals,Braille output, or the like. In response to the warnings, the user maychoose to replace one or more component in the fluid path including forexample the infusion set, tubing, tubing connector, reservoir, stopper,or the like. Other responses that the user might have to an occlusionwarning include: running a self test of the infusion pump, recalibratingthe sensor, disregarding the warning, replacing the infusion pump,sending the infusion pump in for repair, or the like. In alternativeembodiments, when an occlusion is detected, attempts for fluid deliveryare continued, and a warning is provided to the user or otherindividuals.

When using the maximum measurement threshold method, an occlusion isdeclared when the measured force exceeds a threshold. In preferredembodiments, a threshold of 2.00 pounds (0.91 kg) is compared to forcevalues measured by the sensor before delivery of fluid. If a measuredforce is greater than or equal to 2.00 pounds (0.91 kg), one or moreconfirmation measurements are taken before fluid delivery is allowed. Iffour consecutive force measurements exceed 2.00 pounds (0.91 kg), anocclusion is declared. In alternative embodiments, a higher or lowerthreshold may be used and more or less confirmation readings may becollected before declaring an occlusion depending upon the sensor signalto noise level, the electronics signal to noise level, measurementdrift, sensitivity to temperature and/or humidity, the force required todeliver fluid, the maximum allowable bolus, the sensor's susceptibilityto shock and/or vibration, and the like. In further alternativeembodiments, the maximum measurement threshold method is not used.

As mentioned previously, the use of sensors, which provide a spectrum ofoutput levels, rather than a switch, which is capable of providing onlytwo discrete output levels, allows the use of algorithms to detecttrends in the output, and thus, declare an occlusion before the maximummeasurement threshold is reached. In preferred embodiments, the slopethreshold method is used to evaluate trends to provide early occlusiondetection. When using the slope threshold method, an occlusion isdeclared if a series of data points indicate that the force required forfluid delivery is increasing. A slope is calculated for a line passingthrough a series of consecutive data points. If the slope of the lineexceeds a slope threshold, then pressure is increasing in the fluidpath, and therefore, an occlusion may have developed. When nothing isblocking the fluid path, the force measured by the sensor before eachdelivery remains constant.

During fluid delivery, when the drive system moves the stopper forwardwithin the reservoir, the force temporarily and rapidly increases. Thenas the fluid moves out of the fluid path, through the cannula and intothe body, the force returns to a similar level as measured before fluiddelivery was initiated. As an example, a plot of the voltage output,collected at a sample rate of 3 Hz during a series of fluid deliveries,is shown in FIG. 11. The sawtooth appearance of the voltage plot is theresult of the sharp increases and slow decay of the force measured bythe sensor when the drive system is activated followed by fluid flowingfrom the infusion pump or relief due to compliance.

The bottom of each sawtooth represents the static force measured beforefluid delivery is begun. Initially, the fluid path is free ofocclusions. Voltage samples measured before line 210 are values measuredbefore the fluid path is blocked. The static force measurements takenbefore the fluid path is blocked are similar, and the slope of a line212 drawn through those static force measurements is approximately ornear zero. In other words, there is no occlusion in the fluid path, andthe fluid pressure returns to the same offset value after each delivery.However, after line 210 (when the fluid path is blocked) the staticforce increases after each fluid delivery. The slope of a line 214 drawnthrough the static force measurements after line 210, is now greaterthan zero. The voltage output is generally proportional to the forceapplied to the sensor.

In preferred embodiments, if the measured static force increases by morethan 0.05 pounds (0.23 kg) on average for each of 15 consecutivedeliveries, an occlusion is declared. Given the example shown in FIG.11, if we assume that a voltage output of 1.0 volts is equal to or lessthan 1.0 pound (0.45 kg) of force on the sensor, then it is clear thatthe slope threshold method is likely to declare the occlusionsignificantly sooner than the maximum measurement value of 2.00 pounds(0.91 kg) is obtained. The slope threshold method would declare anocclusion at about line 216, while the maximum measured threshold methodwould not have declared an occlusion even at the highest measurement onthe page. Lowering the maximum measurement threshold might help todeclare an occlusion sooner, but the drive systems in some infusionpumps are likely to have more friction than others. And the friction ofthe drive train may change over an extended period of use. So, if themaximum measurement threshold is set too low, occlusions maybeinadvertently declared in pumps that have higher than average frictionin the drive system.

In alternative embodiments, larger or smaller changes in force over alarger or smaller number of measurements is used to declare an occlusiondepending upon the force measurement resolution, the signal to noiseratio in the voltage output, friction in the drive train, the maximumallowable delivery, or the like. In further alternative embodiments, theslope is calculated from force or voltage values that are collected attimes other than prior to fluid delivery such as, after fluid delivery,during fluid delivery, randomly, continuously, or the like. In stillfurther alternative embodiments, other algorithms may be employed tocalculate a slope or evaluate the difference between one measurement andanother, such as using differential values rather than actual measuredvalues, calculating the derivative of measured values, using a subset ofpoints across the range of points to calculate the slope, using curvefitting equations, employing smoothing, clipping or other filteringtechniques, or the like.

In particular alternative embodiments, the static force must exceed aminimum threshold and the slope must exceed a maximum value for anocclusion to be declared. For example, an occlusion is only declared ifthe last force measurement is greater than 1.00 pound (0.45 kg) and theslope is greater than 0.05 on average for each of the last 15measurements (generally associated with the last 15 deliveries).

In particular embodiments, an occlusion is declared if an average slope(A) exceeds a slope threshold of 0.05. The Current Slope (S) iscalculated as:

S=F(0)−F(−5).

Where F(0) is a current force measurement, and F(−5) is a forcemeasurement taken 5 measurements previously.

And the Average Slope (A) is:

A=A(−1)+W*(S−A(−1)).

Where A(−1) is the average slope calculated at the previous forcemeasurement, W is a weighting factor of 0.30, and S is the currentslope.

In other particular embodiments, and occlusion is declared if theaverage slope (A) is greater than a slope threshold of 0.05 for 15measurements in a row. And if the average slope (A) drops below 0.05 for4 measurements in a row, then restart counting. Measurements are takenjust prior to each delivery. A delivery is defined as an incrementalmotor activation to dispense a controlled dose of fluid. In particularembodiments, after each measurement, a counter is incremented if theaverage slope exceeds the slope threshold. If the counter reaches adetection count value, then an occlusion is declared.

In alternative embodiments, the measured values used to calculate thecurrent slope are separated by a greater or smaller number ofmeasurements. In further alternative embodiments, the weighting factor Wis larger or smaller depending on the previous average slope A(−1), thecurrent force reading F(0), the accuracy of the measurements, and thelike. And in other alternative embodiments, the slope threshold isgreater or smaller depending on the concentration of the fluid, themaximum allowable bolus, the sensor accuracy, the signal to noise ratio,and the like. In still further alternative embodiments, one or more ofthe measured force values must meet or exceed 1.00 pound before theslope threshold method can declare an occlusion. For example, in someembodiments, the last four force measurements must be greater than 1.00pound and the average slope must exceed 0.05 over the last 15 forcemeasurements to declare an occlusion. In other alternative embodiments,the detection count value may be higher or lower depending on the sensoraccuracy, the level of shock and vibration effects, the required rangeof measurement, and the like.

In further particular embodiments, the number of deliveries permeasurement is dependent on the concentration of the fluid beingdelivered. For example, when delivering a U200 insulin formula, ameasurement is taken with each delivery, when delivering a U100 insulinformula, a measurement is taken every two deliveries, and whendelivering a U50 insulin formula, a measurement is taken every 4deliveries.

In alternative embodiments, other algorithms are used to calculate aslope from the sensor measurements to compare to a slope threshold.Other algorithms include, but are not limited to, a least squares linefit through a number of measurements, averaging two or more groups ofmeasurements and then calculating the slope of a line through theaveraged values, regression algorithms, or the like.

In still other alternative embodiments, the current force measurement iscompared to one or more previous force measurements, or to a trendobserved from force measurements, to determine whether the current forcemeasurement is valid (representative of a force applied to the drivetrain by the motor). If the current force measurement is not valid, itis ignored, replaced, re-measured, or the like.

While the specific embodiments illustrated herein generally pertain tomedication infusion pumps, the scope of the inventions in one aspect ismuch broader and may include any type of fluid pump medical system.

In particular embodiments, the sensor is used to detect the removal ofone or more components in the fluid path such as disconnecting theinfusion set, disconnecting the tubing, or the like. During normaloperation, the sensor is subjected to a nominal force due to the sum ofthe system frictional components, the hydrodynamic forces associatedwith delivering a fluid through tubing, and the backpressure associatedwith the infusion set inserted in the patient. The nominal force isrepresented by a voltage offset such as represented by line 212 in FIG.11. If a component in the fluid path were removed, the fluidbackpressure would decrease thereby reducing the nominal force on thesensor. The infusion pump provides a warning to the user when thenominal force on the sensor decreases below a threshold, decreases by aparticular percentage, decreases over a series of measurements, or thelike. In alternative embodiments, larger or smaller decreases in thenominal force on the sensor are used to detect leaks in the fluid path.

In other particular embodiments, a sensor is used to detect when areservoir is empty. An encoder is used to measure motor rotation. Theencoder counts increase as the motor operates to move a stopper deeperinto the reservoir. The encoder counts are used to estimate when thestopper is nearing the end of the reservoir. Once the encoder counts arehigh enough, if an occlusion is detected due to increased force on thesensor, the reservoir is declared empty.

In other particular embodiments, a sensor 706 is used to detect when aslide 711 is properly seated with a stopper 714, as shown in FIG. 7(a).The reservoir 715 containing the stopper 714 is filled with fluid beforeit is placed into an infusion pump 701. The stopper 714 has pliableinternal threads 713 designed to grip external threads 712 on the slide711. The stopper 714 and slide 711 do not need to rotate with respect toeach other to engage the internal threads 713 with the external threads712. In fact, in particular embodiments, the internal threads 713, andthe external threads 712, have different thread pitches so that somethreads cross over others when the slide 711 and stopper 714 are forcedtogether. Once the reservoir 715 is placed into the infusion pump 701, amotor 705 is activated to move the slide 711 into the reservoir 715 toengage the stopper 714. As the threads 712 of the slide 711 firstcontact the threads 713 of the stopper, a sensor 706 detects an increasein force. The force continues to increase as more threads contact eachother. When the slide 711 is properly seated with the stopper 714, theforce measured by the sensor 706 increases to a level higher than theforce needed to engage the internal threads 713 with the externalthreads 712. During the seating operation, if the force sensed by thesensor 706 exceeds s seating threshold, the motor 705 is stopped untilfurther commands are issued. The seating threshold is generally about1.5 pounds (0.68 kg). In alternative embodiments higher or lower seatingthresholds may be used depending on the force required to mate the slidewith the stopper, the force required to force fluid from the reservoir,the speed of the motor, the sensor accuracy and resolution, or the like.

In still other particular embodiments, other force thresholds are usedfor other purposes. During priming for example, a threshold of about 4pounds (2 kg) is used. In alternative embodiments, forces greater thanabout 4 pounds are used to detect shock loads that may be damaging to aninfusion pump.

Typically, over a long enough period of operation, sensors suffer fromdrift. In preferred embodiments, drift measurements are taken though thelife of a statistically significant number of sensors to generate adrift curve. The drift curve is used to compensate for drift in sensorsused in infusion pumps. For example, a lookup table of force offset (dueto drift) over operation time is stored in the infusion pump. The offsetvalues are used to compensate the force measurements over time. Inalternative embodiments, the drift is characterized by an equationrather than a lookup table. In other alternative embodiments, the sensoris periodically re-calibrated. In still other alternative embodiments,the sensor does not drift or the drift is insignificant enough that nocompensation is needed.

In further alternative embodiments, drift is compensated relative to thenumber of deliveries, the number of reservoir replacements, the integralof the forces placed on the sensor, or the like.

Particular sensors used to detect occlusions suffer from temperatureand/or humidity shifts. In preferred embodiments, the infusion pumpincludes humidity and/or temperature sensors. Measurements from thehumidity and/or temperature sensors are used to compensate the sensoroutput. In alternative embodiments, humidity and/or temperaturecompensation is not needed.

The use of sensors for detecting characteristics of the drive system andthe fluid containing assembly are not limited to the infusion pumps anddrive systems shown in the figures. Moreover, the type of sensor neednot be confined to a force sensitive resistor as described in preferredembodiments.

In alternative embodiments, a capacitive sensor 1401 is used, such asshown in FIG. 12. A dielectric material 1402 is disposed between aconductive proximate plate 1403 and a conductive distal plate 1404. Thedistal plate 1404 is secured to a pump housing 1405 or alternatively, toany other stationary component of a medication infusion pump. Theproximate plate 1403 is in contact with a drive system lead screw 1406.Alternatively, the proximate plate 1403 could be in contact with a pumpmotor or any other dynamic drive train component that is subjected to areactive force correlated to reservoir fluid pressure variations.

As the force applied to the drive train increases, the lead screw 1406applies greater force to the proximate plate 1403 moving it closer tothe distal plate 1404, and partially compressing the dielectric material1402. As the gap across the dielectric material 1402 decreases, thesensor capacitance increases. The capacitance is expressed by therelationship: $C = \frac{k\quad ɛ_{0}A}{d}$

where C is the capacitance, ε_(o) is the permittivity constant (of freespace), A is the surface area of the conductive plates, and d is thedistance between the conductive plates. Electrical leads 1407 connectthe proximate plate 1403 and the distal plate 1404 to the electronicssystem (not shown), which measures the varying capacitance. Theelectronics system and sensor are calibrated by applying known forces tothe drive train. Once calibration is complete, the electronics systemconverts sensor capacitance to force measurements.

In another alternative embodiment, a cylindrical capacitive sensor 1501includes a conductive rod 1502, a dielectric inner ring 1503 and aconductive outer ring 1504, as shown in FIG. 13. The conductive rod 1502is connected to a drive system lead screw (not shown). Alternatively,the conductive rod 1502 could be connected to any other dynamic drivetrain component that experiences movement correlated to a reservoirfluid pressure. Conductive leads (not shown) electrically connect therod 1502 and the outer ring 1504 to the system electronics.

In particular embodiments, as the fluid pressure increases, the leadscrew is axially displaced, which in turn moves the rod 1502 furtherinto the opening 1505 formed by the rings 1503 and 1504. Thus, thesurface area of the capacitor increases, thereby increasing capacitanceaccording to the relationship:$C = \frac{2\pi \quad k\quad ɛ_{0}l}{\ln \left( \frac{b}{a} \right)}$

where C is the sensor capacitance, l is the length of the rod 1502 thatis enclosed by the rings 1504 and 1503, a is the radius of the rod 1502,b is the internal radius of the outer ring 1504 and ε₀ is thepermittivity of free space. Once calibrated, the electronics systemconverts the measured sensor capacitance to a force measurement.

Although the use of force sensitive resistors and capacitive sensorshave been described above, it should be appreciated that the embodimentsdisclosed herein include any type of sensor that can provide least threedifferent levels of output signal across the range of intended use.Sensors may be positioned within various embodiments of drive trains tomeasure either a force applied to a drive train component, a change inposition of a drive train component, a torque applied to a drive traincomponent, or the like.

For example, in alternative embodiments a piezoelectric sensor is usedto produce varying voltages as a function of varying forces applied to adrive train component. In particular alternative embodiments, thepiezoelectric sensor is made from polarized ceramic or PolyvinylideneFloride (PVDF) materials such as Kynar®, which are available from AmpIncorporated, Valley Forge, Pa.

In other alternative embodiments, multi-switch sensors are used. Adistinction is made between switches, which have only two distinctoutput levels, versus sensors, which have more than two output levels.But, multi-switch sensors are sensors made from two or more discreteswitches having different actuation set points. Thus, these multi-switchsensors have at least three output levels. In particular alternativeembodiments, a sensor 1601 is comprised of five series mounted switches1602 a-1602 e, each of which has a different set-point, as shown in FIG.14(a). A first switch 1602 a is positioned in contact with a lead screw1603, or alternatively, any other drive train component that issubjected to a force correlated with a reservoir fluid pressure. At theopposite end of the series of switches 1602 a-1602 e, a last switch 1602e is secured to a pump housing 1604 or alternatively, to any otherstationary component of an infusion pump. Conductive leads 1605 areattached to each of the switches 1602 a-1602 e. As the force applied tothe lead screw 1603 increases, the switches 1602 a-1602 e are triggeredone after another as their set points are reached. The electronicssystem (not shown) monitors each switch. In further particularembodiments, the sensor resolution is dependent on the number ofswitches and the relative force required for triggering each switch, therange of measurements needed, and the like.

In still other alternative embodiments, the sensor incorporates amulti-switch design where a series of switches 1607 a-1607 e areelectrically connected in series, as shown in FIG. 14(b). An electricallead 1608 connects a first switch 1607 a to the electronics system (notshown). Leads 1609 connect each switch 1607 a to 1607 e in series.Finally, lead 1610 connects a last switch 1607 e to the electronicssystem. All of the switches 1607 a-1607 e are electrically connectedsuch that continuity exists through each switch regardless of whether aswitch is in a first position or a second position (on or off).Otherwise, the series electrical connection would be broken when aswitch is opened.

In particular alternative embodiments, each of the switches 1607 a-1607e have a first position and a second position, as shown in FIG. 14(c).When in the first position, each switch connects the circuit through afirst resistor 1611 a-1611 e, each of which has a value of R1 ohms. Wheneach switch is subjected to a force at its respective set point, itmoves to its second position thereby disconnecting from the firstresistor 1611 a-1611 e, and closing the circuit through a secondresistor 1612 a-1612 e, each having a value of R2 ohms. And R1 does notequal R2. Thus, depending upon the position of each of the switches 1607a-1607 e, a different over-all circuit resistance is measured by theelectronics system corresponding to the force applied to a drive traincomponent. In further particular alternative embodiments, while theresistance of all of the first resistors R1 is greater than or less thanthe resistance of all of the second resistors R2, the resistance of eachof the first resistors R1 are not equal to each other, and/or theresistance of each of the second resistors R2 are not equal to eachother. In other particular embodiments, a switch with the highest setpoint may not include resistors, but may simply be an on/off switch. Instill other embodiments, other electrical components and/or arrangementsare used, such as a parallel circuit shown in FIG. 15(c).

In alternative embodiments, an infusion pump uses a sensor made of twoor more multi-switches that are arranged in a parallel circuit. Inparticular alternative embodiments, a sensor 1701 has five switches 1702a-1702 e arranged in parallel, each with a different set point, as shownin FIGS. 15(a) and 15(b). The switches 1702 a-1702 e are mechanicallyarranged in parallel such that one side of all five switches 1702 a-1702e is in contact with a pump housing 1703, or another member that isstationary with respect to the housing. The opposite side of each of theswitches 1702 a-1702 e is secured to a plate 1704. A drive traincomponent, such as a lead screw 1705, directly or indirectly appliesforce to the plate 1704. The force is correlated to the fluid pressurein the reservoir (not shown). As the lead screw 1705 moves in directiond, each one of the switches 1702 a-1702 e will close at different setpoints depending upon the amount of force exerted on the plate 1704 bythe lead screw 1705.

The switches 1702 a-1702 e can be electrically connected to each otherand to the system electronics in any number of ways. For example, eachswitch could be independently connected to the system electronics.Alternatively, the switches 1702 a-1702 e could be electricallyconnected in series. In other embodiments each switch 1702 a-1702 e isassociated with a resistor 1707 a-1707 e, and the switches are connectedin parallel, as shown in FIG. 15(c). A conductive lead 1708 provides aninput signal from an electronics system (not shown) to the parallelarray of switches 1702 a-1702 e. When the force across a switch reachesthe switch set point, the switch closes, and current flows through theresistor 1707 a-1707 e associated with the switch 1702 a-1702 e througha lead 1709, and back to the electronics system. As differentcombinations of switches close, different resistors are placed inparallel in the network, thus changing the impedance of the network. Theimpedance is measured by the electronics system and converted tomeasured force that is correlated to fluid pressure.

While the previously described embodiments have illustrated the couplingof various types of sensors to components at the end of a drive train,the scope of the present invention is by no means limited to suchlocations. Other embodiments include the placement of sensors at or nearthe front end of a drive train.

In particular embodiments, a slide assembly 1807 is comprised of a thin,dome-shaped cap 1802, mounted on a support assembly 1803, and secured toa lead screw 1804, as shown in FIG. 16. A strain gauge sensor 1801 ismounted on the cap 1802. The cap 1802 is constructed of a resilientmaterial, such as silicone, and is in contact with a stopper 1805, whichis slidably positioned in a reservoir 1806. As the lead screw 1804advances, the support assembly 1803 and cap 1802 move axially to contactthe stopper 1805, and cause the stopper 1805 to move axially forcingfluid from the reservoir 1806.

The cap 1802 deflects as it is pressed against the stopper 1805. And asthe cap 1802 deflects, the dimensions of the strain gauge sensor 1801are changed, thereby changing the strain gauge impedance. As fluidpressure in the reservoir 1806 increases, the cap 1802 deflectionincreases, which changes the impedance of the strain gauge sensor 1801.Thus, the strain gauge sensor output impedance is related to the forceimposed on the stopper 1805, which is correlated with the reservoirfluid pressure. The electronics system is calibrated to convert themeasured strain gauge sensor output impedance to force on the drivetrain or fluid pressure.

Having the sensor in direct contact with the stopper 1805 amelioratesthe effects of dimensional tolerance stack-up and frictional forceswithin the drive train. This can allow for a more accurate measurementof the pressures within the reservoir 1806. Additionally, since thestrain gauge sensor 1801 can provide a range of output levels,software/firmware can be used to set a threshold value that isappropriate for the particular device or drug being infused.Furthermore, over time, the system can calibrate or zero the straingauge sensor 1801 when there is no reservoir 1806 in place in order toavoid undesirable effects from drift, creep, temperature, humidity, orthe like.

Other embodiments of the present invention involving a sensor mounted ator near the front of the drive train are shown in FIGS. 17 to 20.

In a particular embodiment, a slide 1908 includes a strain gauge sensor1901, a bellows 1903, and a support assembly 1904, as shown in FIG. 17.The bellows 1903 has a proximate wall 1902 a, a distal wall 1902 b, anda flexible sidewall 1902 c. The strain gauge sensor 1901 is mounted onthe distal wall 1902 b. At least a portion of the perimeter of thedistal wall 1902 b supported by the support assembly 1904. And thesupport assembly 1904 is secured to a lead screw 1905. The distal wall1902 b is constructed of a deflectable resilient material, such assilicone, so that as pressure is placed against the proximate wall 1902a, the distal wall 1902 b deflects toward the lead screw 1905. Thebellows 1903 is driven forward by the lead screw 1905 and supportassembly 1904 to push on a stopper 1906 that is slidably positioned in areservoir 1907. As the lead screw 1905 continues to advance, the bellows1903 pushes on the stopper 1906 to force fluid from the reservoir 1907.The bellows 1903 may be filled with a fluid to improve the transfer ofpressure from the proximate wall 1902 a to the distal wall 1902 b. Theamount of distal wall 1902 b deflection is correlated with the forcerequired to move the stopper 1906. The strain gauge sensor output iscorrelated with the amount of distal wall 1902 b deflection. Theelectronics system converts the strain gauge sensor output to anestimate of force or pressure exerted by the drive system to deliverfluid.

In similar particular embodiments, a slide 2009 is comprised of a straingauge sensor 2001, a support assembly 2004 and a resilient bellows 2003having a threaded member 2006, as shown in FIG. 18. The strain gaugesensor 2001 is mounted on a distal wall 2002 of the bellows 2003. Thesupport assembly 2004 supports at least a portion of the perimeter ofthe distal wall 2002 of the bellows 2003, and couples a lead screw 2005with the bellows 2003. The threaded member 2006 of the bellows 2003 isremovably secured to a stopper 2007 that is slidably positioned in areservoir 2008. This allows for bi-directional displacement of thestopper 2007 by the drive system as well as helping to prevent theunintended advancement of the stopper 2007 due to forces on thereservoir 2008 other than lead screw 2005 advancement, such asdifferential air pressure, or the like. As the stopper 2007 is pushed orpulled by the drive system, the distal wall 2002 is deflected one way oranother. The output of the strain gauge sensor 2001 varies with thedeflection of the distal wall 2002, and the electronic system convertsthe strain gauge sensor output to estimates of force or pressure appliedto the stopper 2007 by the drive system.

In an alternative embodiment, external threads 2115 of a lead screw 2101are engaged with the internal threads 2116 of a slide 2102 to convertthe rotational motion of the lead screw 2101 to translational motion ofthe slide 2102, as shown in FIG. 19. The slide 2102 has a nose 2103formed by a relatively stiff generally cylindrical sidewall 2117 and aproximate nose wall 2104 made of a flexible material such as silicone. Astrain gauge sensor 2105 is secured to the proximate nose wall 2104. Theslide 2102 is removably coupled to a stopper 2106 slidably positioned ina fluid reservoir 2107. The stopper 2106 has a cavity 2112 formed by aninternally threaded cylindrically-shaped sidewall 2110, which forms awater-tight seal with the reservoir 2107, and a flexible proximate wall2108. The cavity 2112 is adapted to receive the nose 2103, so that theproximate wall 2108 of the cavity 2112 abuts the proximate nose wall2104 of the nose 2103. The nose sidewall 2117 has external threads 2113for removably engaging the internal threads 2114 on the sidewall 2110 ofthe stopper cavity 2112. The threaded coupling between the slide 2102and the stopper 2106 enables the drive system to move the stopper 2106bi-directionally. A reinforcing ring 2109 is disposed in the stoppersidewall 2110 to provide the necessary stiffness to maintain africtional fit between the stopper 2106 the reservoir 2107, therebyenhancing a watertight seal. In further alternative embodiments, thereinforcing ring 2109 is not needed.

As the flexible proximate wall 2108 of the stopper 2106 deflects due tofluid pressure, it contacts the proximate nose wall 2104 causing it todeflect, thus deflecting the strain gauge sensor 2105. This provides ameasurement of the pressure within the reservoir 2107 independent of theforce used to drive the stopper 2106. This sensor placement provides atrue indicator of pressure within the reservoir 2107. The frictionalforces between the stopper 2106 and the reservoir 2107, as well asbetween other drive train components are not measured, and therefore donot affect the measurement of the fluid pressure.

In particular alternative embodiments, measurements from the straingauge sensor 2105 are used to confirm correct reservoir 2107installation. If the reservoir 2107 is installed into the infusion pumpproperly and the slide 2102 is fully engaged with the stopper 2106within the reservoir 2107, then the stopper 2106 applies at least aslight contact with the proximate nose wall 2104 imparting a preload onthe strain gauge sensor 2105. If the reservoir 2107 is not inserted (orfully inserted), then no pre-load is detected, and the electronicssystem provides a warning to the user.

In other embodiments, shear forces are measured to provide an indicationof fluid pressure. A slide assembly 2207 is comprised of a supportassembly 2202, piezoelectric shear sensors 2203, and a nose 2204 havinga proximate nose wall 2204 a and a sidewall 2204 b, a shown in FIG. 20.A lead screw 2201 is secured to the support assembly 2202. Thepiezoelectric shear sensors 2203 are disposed between the supportassembly 2202 and the sidewall 2204 b of the nose 2204. A stopper 2205is slidably mounted in a reservoir 2206. The stopper 2205 has aproximate wall 2209 and a generally cylindrical sidewall 2210 that forma cavity 2208 adapted to receive the nose 2204 portion of the slideassembly 2207. However, in alternative embodiments, the stopper 2205does not have a cavity. Rather, the nose 2204 abuts the distal wall 2210of the stopper 2205.

Returning to FIG. 20, as the lead screw 2201 advances, the supportassembly 2202 and nose 2204 move axially to engage the stopper 2205, andthen move the stopper 2205 into the reservoir 2206, forcing fluid fromthe reservoir 2206.

The force required to move the stopper 2205 is measured as shear forcesplaced on the piezoelectric shear sensors 2203. As the pressure on thestopper 2205 increases, the shear forces between the nose 2204 and thesupport assembly 2202 increase and apply shear force to the sensors2203.

The previously described embodiments generally measure fluid pressure orforces exerted in an axial direction down the drive train. Alternativeembodiments of the present invention however, measure a torque appliedto a drive system component as an indication of the fluid pressurewithin a reservoir.

In particular embodiments, a motor 2301 (or a motor with an attachedgear box) has a drive shaft 2302 engaged to drive a set of gears 2303.The motor 2301 generates a torque powering the drive shaft 2302 indirection d, as shown in FIG. 21. The drive shaft 2302 rotates the gears2303 to transfer the torque to a lead screw 2304, rotating the leadscrew 2304 in the direction d′. The lead screw 2304 is mounted on abearing 2305 for support. The threads of the lead screw 2304 are engagedwith threads (not shown) in a slide 2306. The slide 2306 is engaged witha slot (not shown) in the housing (not shown) to prevent the slide 2306from rotating, but allowing it to translate along the length of the leadscrew 2304. Thus, the torque d′ of the lead screw 2304 is transferred tothe slide 2306 causing the slide 2306 to move in an axial direction,generally parallel to the drive shaft 2302 of the motor 2301. The slide2306 is in contact with a stopper 2307 inside a reservoir 2308. As theslide 2306 advances, the stopper 2307 is forced to travel in an axialdirection inside the reservoir 2308, forcing fluid from the reservoir2308, through tubing 2309, and into an infusion set 2310.

Should an occlusion arise, the stopper 2307 is forced to advance, andpressure in the reservoir 2308 increases. The force of the stopper 2307pushing against the fluid results in a reaction torque d″ acting on themotor 2{tilde over (□)}₁. In particular embodiments, sensors are used tomeasure the torque d″ applied to the motor 2301, and the sensormeasurement is used to estimate the pressure in the reservoir 2308.

In particular embodiments, a motor 2401 has a motor case 2402, aproximate bearing 2403, a distal bearing 2404, a motor shaft 2408, and agear 2405, as shown in FIGS. 22(a and b). The motor 2401 is secured to ahousing (not shown) or other fixed point by a beam 2406. One end of thebeam 2406 is secured to the motor case 2402 at an anchor point 2410, andthe other end of the beam 2406 is secured to the housing (not shown) ata housing anchor point 2409. A strain gauge sensor 2407 is mounted onthe beam 2406.

Each end of the motor shaft 2408 is mounted on the bearings 2403 and2404 that provide axial support but allow the motor shaft 2408 and motor2401 to rotate. The beam 2406 supplies a counter moment in the directiond′ that is equal in magnitude and opposite in direction to the motordriving torque d. As the torque produced by the motor 2401 increases,the reaction moment d″ in the beam 2406 increases thereby increasing thestrain within the beam 2406 and causing the beam 2406 to deflect. Thestrain gauge sensor 2407 mounted on the beam 2406 is used to measuredeflection of the beam 2406. The electronics system (not shown) convertsthe strain gauge sensor measurements to estimates of fluid pressure in areservoir (not shown) or force acting on the drive train (not shown).

This method of measurement provides information about the pressurewithin the reservoir (and frictional stack-up), as well as informationabout the drive train. If for example, there were a failure within thedrive train such as, in the gearing, bearings, or lead screw interface,the torque measured at the strain gauge sensor 2407 would detect thefailure. In further embodiments, the strain gauge 2407 is used toconfirm motor activation and fluid delivery. During normal fluiddelivery, the measured moment increases shortly while the motor isactivated, and then decreases as fluid exits the reservoir relievingpressure and therefore the moment. The electronics system is programmedto confirm that the measured moment increases during motor activationand that the moment decreases back to a resting state after the motor isno longer powered

In still further embodiments, a beam provides the necessary complianceto protect a drive system from a rewind hard stop. A motor is used torewind a slide in preparation to replace a reservoir. However, once theslide is fully retracted, a hard stop at full motor speed could damageor reduce the life of drive system components. The beam absorbs theenergy when the slide reaches the fully retracted position, withoutdamaging the drive system.

A strain gauge sensor can work in several modes common to strain gaugesensor technology. For example, the strain gauge sensor could be mountedsuch that it measures tension or compression, or bending. In addition, astrain gauge sensor could be mounted to compensate for temperaturevariances and other system noises. Furthermore, the designs of FIGS.19-22(b) are not limited to strain gauge sensor technology.Piezoelectric, capacitive, or magnetic sensors could be used as well.

In alternative embodiments, a motor 2501 has a case 2502, a proximatebearing 2503, a distal bearing 2504, a motor shaft 2507, and a gear2505, as shown in FIG. 23. The portion of the drive train not shown inFIG. 23 is similar to that shown in FIG. 21. The proximate bearing 2503is disposed on one side of the pump motor 2501, and the distal bearing2504 is disposed on the opposite side of the pump motor 2501. Motormounts 2506 secure the case 2502 to the housing 2509 (or other fixedpoint). Piezoelectric shear mode sensors 2508 are secured to the mounts2506. As the reaction torque d′ increases due to an increase in theapplied drive torque d, shear stress in the motor mounts 2506 increase.The sensors 2508 in turn provide a voltage correlated to the drivetorque d. As discussed previously, the drive torque d is correlated tothe fluid pressure in a reservoir (not shown).

Although the pump drive systems described above incorporate theplacement of sensors at certain locations on pump drive trains,alternative embodiments of the present invention include sensors, whichare coupled to any dynamic drive train component, in order to measurefluid pressure in a pump drive system.

While the description above refers to particular embodiments of thepresent invention, it will be understood that many modifications may bemade without departing from the spirit thereof. The accompanying claimsare intended to cover such modifications as would fall within the truescope and spirit of the present invention.

The presently disclosed embodiments are therefore to be considered inall respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims, rather than theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are therefore intended to be embracedtherein.

What is claimed is:
 1. An occlusion detection system for detecting anocclusion in a fluid path of an infusion pump with a reservoircontaining fluid for delivering fluid to a user, the occlusion detectionsystem comprising: a housing; a motor contained within the housing; oneor more drive train components that react to stimulus from the motor toforce a fluid from a reservoir into the user; a sensor positionedbetween the motor and a housing component to measure a parameterassociated with the motor or a drive train component, wherein one ormore components including the sensor are stacked between the motor andthe housing component, and wherein the housing component is positionedto remove space between the one or more components before the housingcomponent is attached to the housing, wherein the sensor produces threeor more output levels across a range of measurements; and an electronicssystem that processes the three or more output levels to declare when anocclusion exists.
 2. An occlusion detection system according to claim 1,wherein the sensor measures a force proportional to a force applied to adrive train component.
 3. An occlusion detection system according toclaim 2, wherein the drive train component is a lead screw.
 4. Anocclusion detection system according to claim 2, wherein the drive traincomponent is a slide.
 5. An occlusion detection system according toclaim 1, wherein the sensor is a force sensitive resistor.
 6. Anocclusion detection system according to claim 1, wherein the sensor is acapacitive sensor.
 7. An occlusion detection system according to claim1, wherein the sensor is a strain gauge.
 8. An occlusion detectionsystem according to claim 1, wherein the sensor is a piezoelectricsensor.
 9. An occlusion detection system according to claim 1, whereinthe electronics system uses a maximum measurement threshold method todeclare when an occlusion exists.
 10. An occlusion detection systemaccording to claim 9, wherein a measurement threshold is at least 2.00pounds.
 11. An occlusion detection system according to claim 1, whereinthe electronics system uses a slope threshold method to declare when anocclusion exists.
 12. An occlusion detection system according to claim11, wherein a slope threshold is about 0.05 pounds per measurement. 13.An occlusion detection system according to claim 1, wherein theelectronics system uses a maximum measurement threshold method, and aslope threshold method to declare when an occlusion exists.
 14. Anocclusion detection system according to claim 1, wherein one or moremeasurements must exceed a minimum level to declare that an occlusionexists.
 15. An occlusion detection system according to claim 1, whereinthe measured parameter is correlated with a fluid pressure in thereservoir.
 16. An occlusion detection system according to claim 1,wherein VHB adhesive is positioned between the motor and the housingcomponent.
 17. An occlusion detection system according to claim 1,wherein the sensor is a multi-switch sensor.
 18. An occlusion detectionsystem for detecting an occlusion in a fluid path of an infusion pumpwith a reservoir containing fluid for delivering fluid to a user, theocclusion detection system comprising: a housing; a motor containedwithin the housing; one or more drive train components that react tostimulus from the motor to force a fluid from a reservoir into the user;a sensor positioned to measure a parameter associated with the motor ora drive train component, wherein the sensor measures tension orcompression on a beam proportional to a torque applied to the motor, andwherein the sensor produces three or more output levels across a rangeof measurements; and an electronics system that processes the three ormore output levels to declare when an occlusion exits.
 19. An occlusiondetection system according to claim 18, wherein the drive traincomponent is a beam.
 20. An occlusion detection system according toclaim 18, wherein the drive train component is one or more mounts. 21.An occlusion detection system for detecting an occlusion in a fluid pathof an infusion pump with a reservoir containing fluid for deliveringfluid to a user, the occlusion detection system comprising: a housing; amotor contained within the housing; one or more drive train componentsthat react to stimulus from the motor to force a fluid from a reservoirinto the user; a sensor positioned to measure a parameter associatedwith the motor or a drive train component, wherein the sensor measurestension or compression proportional to a pressure applied to a drivetrain component, and wherein the sensor produces three or more outputlevels across a range of measurements; and an electronics system thatprocesses the three or more output levels to declare when an occlusionexists.
 22. An occlusion detection system according to claim 21, whereinthe drive train component is a bellows.
 23. An occlusion detectionsystem according to claim 21, wherein the drive train component is acap.
 24. An occlusion detection system for detecting an occlusion in afluid path of an infusion pump with a reservoir containing fluid fordelivering fluid to a user, the occlusion detection system comprising: ahousing; a motor contained within the housing; one or more drive traincomponents that react to stimulus from the motor to force a fluid from areservoir into the user; a sensor positioned to measure a parameterassociated with the motor or a drive train component, wherein the sensorproduces three or more output levels across a range of measurements; andan electronics system that processes the three or more output levels todeclare when an occlusion exits, wherein the electronics systemprocesses the sensor output levels to determine when the reservoir isempty.
 25. An occlusion detection system for detecting an occlusion in afluid path of an infusion pump with a reservoir containing fluid fordelivering fluid to a user, the occlusion detection system comprising: ahousing; a motor contained within the housing; one or more drive traincomponents that react to stimulus from the motor to force a fluid from areservoir into the user; a sensor positioned to measure a parameterassociated with the motor or a drive train component, wherein the sensorproduces three or more output levels across a range of measurements; andan electronics system that processes the three or more output levels todeclare when an occlusion exists, wherein the electronics systemprocesses the sensor output levels to determine when a stopper contactsan end of the reservoir.
 26. An occlusion detection system for detectingan occlusion in a fluid path of an infusion pump with a reservoircontaining fluid for delivering fluid to a user, the occlusion detectionsystem comprising: a housing; a motor contained within the housing; oneor more drive train components that react to stimulus from the motor toforce a fluid from a reservoir into the user; a sensor positioned tomeasure a parameter associated with the motor or a drive traincomponent, wherein the sensor produces three or more output levelsacross a range of measurements; and an electronics system that processesthe three or more output level to declare when an occlusion exists,wherein the electronics system processes the sensor output levels todetermine when a slide is seated in a stopper.
 27. An occlusiondetection system for detecting an occlusion in a fluid path of aninfusion pump with a reservoir containing fluid for delivering fluid toa user, the occlusion detection system comprising: a housing; a motorcontained within the housing; one or more drive train components thatreact to stimulus from the motor to force a fluid from a reservoir intothe user; a sensor positioned to measure a parameter associated with themotor or a drive train component, wherein one or more componentsincluding the sensor are stacked between the motor and the housing, andwherein back-fill material is injected through the housing to removespace between the one or more components and to fill the space betweenthe one or more components and the housing, wherein the sensor producesthree or more output levels across a range of measurements; and anelectronics system that processes the three or more output levels todeclare when an occlusion exists.
 28. A method of detecting an occlusionin an infusion pump for infusing fluid into the body of a user, themethod comprising the steps of: obtaining a measurement from a sensorbefore each fluid delivery; calculating a current slope of a line usingtwo or more measurements; calculating an average slope using a previousaverage slope and the current slope; comparing the average slope to aslope threshold; incrementing a counter when the average slope exceedsthe slope threshold; declaring an occlusion when the counter exceeds adetection count.
 29. The method according to claim 28, wherein the twoor more measurements are not consecutive.
 30. The method according toclaim 28, further comprising the step of restarting the counter when theaverage slope is below the slope threshold.
 31. An occlusion detectionsystem for detecting an occlusion in a fluid path of an infusion pumpwith a reservoir for containing fluid for delivering fluid to a user,the occlusion detection system comprising: a housing; forcing means forforcing fluid from a reservoir containing a fluid; sensing means forsensing a parameter associated with the forcing means for forcing fluidfrom the reservoir to obtain one or more measurements; wherein one ormore components including the sensing means are stacked between theforcing means and a housing component, and wherein the housing componentis positioned to remove space between the one or more components beforethe housing component is attached to the housing, wherein the sensingmeans produces one of three or more output levels for each of the one ormore the measurements; and evaluation means for evaluating the one ofthree or more output levels associated with each of the one or moremeasurements to declare when an occlusion exists.